This invention relates generally to the field of automated apparatus for handling electronic circuit components and, more particularly, to automated apparatus for use in the art of burning-in circuit components prior to their distribution and use. Still More specifically, this invention is directed to automated insertion and removal of electronic integrated circuit ("IC") packages or devices into or out of sockets on printed circuit boards, especially printed circuit boards used for burn-in testing of IC packages or devices and called "Burn-in Boards" or "BIB's".
IC packages or devices (for brevity, hereinafter both being referred to simply as "devices") may be classified according to force required to insert them into their sockets. Direct entry devices require insertion force and include such devices as dual in-line packages ("DIPs"), which comprise a parallelpiped body portion typically having from four to sixty four electrical leads of a generally L-shaped cross-section extending out and down from the opposing sides of the body. The sockets mounted on the burn-in boards may therefore include socket contact slots for receiving electrical leads on DIPs. Another direct entry device is the small outline J-lead chip carrier ("SOJ").
Zero insertion force devices do not require force to insert them into their sockets ("ZIF" sockets). Zero insertion force devices generally are surface mounted devices ("SMD's"). SMD's are gaining in popularity for packaging integrated circuits, because they mount directly to the surface of the printed circuit board, which eliminates expense of drilling mounting holes through the board. SMD's also are in some instances much smaller than DIP's, allowing tighter packaging densities. SMD's include small outline integrated circuits ("SOIC's"), plastic lead chip carriers ("PLCC's"), ceramic leaded chip carriers ("CLCC's"), leadless chip carriers ("LCC's") and, plastic quad flat packs ("PQFP's"). The SOIC also comprises a generally parallelpiped body portion having electrical leads extending from opposing sides of the body. The electrical lead may have either a J-shaped or a S-shaped ("gull wing") cross-section. The PLCC, CLCC, LCC and PQFP's have bodies which have square or rectangular geometry with a relatively thin cross section, giving these IC packages an overall wafer-shaped appearance. In the usual construction, the PLCC, CLCC and PQFP have multiple electrical leads positioned flush with or bent into close proximity with the body of the package, while the LCC has conductive coatings applied at selected areas on the major body surfaces.
SMD's mount to the surface of the boards in SMD sockets. In these sockets, the SMD's lay on the surface of a support in the socket instead of being inserted into slots in the socket as are DIP's. Spring biased socket contacts press against the SMD's leads that extend from the sides of the SM body. One basic type of SMD socket is the ZIF socket in which the spring biased socket contacts are spread apart by depressing a socket lid to allow clearance for SMD placement and removal. Another type is a so called ZIF "over-the-top" cover socket which is hinged to open the socket lid for SMD placement or removal and which includes a latch to secure it shut.
As is well known and detailed somewhat more in my earlier patent, U.S. Pat. No. 4,817,273 and in the references cited therein, IC devices are mass-produced and installed in electronic circuits used in highly sophisticated, complex and costly equipment. As with many mass-produced products, IC devices are prone to failure, in some cases within the first 1000 hours of operation. The complexity of equipment within which such devices are installed makes post-installation failures highly undesirable. Quality and dependability are enhanced substantially by early detection of those IC devices likely to fail in the first few hours of operation, prior to installation of the devices in electronic equipment. One of the methods for detecting flawed IC devices is referred to generally as "burn-in". Burn-in refers generally to the technique in which IC packages or devices are stressed, and sometimes tested, within their physical and electrical limits prior to their sale or distribution, so that those devices likely to become early failures in complicated equipment can be discovered, and so that IC devices, in some cases, can be graded and sorted according to performance specifications. The burn-in technique generally includes loading the IC devices into sockets on burn-in boards; placing the burn-in boards in a chamber whose environment, particularly temperature, is controllable; applying electrical test signals to the boards while subjecting the IC devices to the maximum temperature reading for them; removing the burn-in board from the chamber; and unloading the IC devices from the burn-in boards. In addition, it is sometimes desirable to sort the IC devices by performance grade after burn-in.
The burn-in test processes however, although successful in reducing expenses associated with flawed IC devices, are not themselves without expense. Substantial capital expenditures are necessary to purchase or to construct burn-in chambers, burn-in boards, and test equipment. Personnel must be employed and trained to operate the equipment and to monitor the time-consuming processes. So substantial are the investments that independent businesses provide burn-in and test services to a variety of manufacturers. Cost effectiveness of the burn-in and test processes is therefore essential.
One means of improving the cost effectiveness of the burn-in and test processes is to reduce labor expenses and to improve efficiency and quality control through the use of automation. Accordingly, efforts have been made to automate various aspects of the burn-in process, as shown, for example, by U.S. Pat. Nos. 4,320,805; 4,439,917; 4,584,764; 4,567,652; 4,660,282; 4,780,956; 4,781,494; 4,801,234; and 4,817,273; and also West Germany Patent Application DE 8,626,502 and Great Britain Patent Application GB 2,157,275A.
Automated handling enables the use of a computer to track and document the progress of each IC devices through the burn-in process. In situations involving a high volume of IC devices for burn-in, automated handling equipment may be used to achieve a higher through-put of IC devices more efficiently than could be achieved otherwise. A single automated loader, for example, can easily replace a goodly number of very efficient employees assigned to the tedious task of loading burn-in boards. In any situation, automated handling equipment provides improved reliability and consistency of work product.
None of the prior methods of automated loading or unloading provide the advantages of my present invention, the features and benefits of which will become apparent from the detailed descriptions which follow after I first summarize the invention.